Effect of annealing treatment on microstructure and residual stress evolution in a selective laser melted Ni-based superalloy

The ZGH452 alloy possesses outstanding high-temperature strength, corrosion resistance, and fatigue durability, offering strong potential for aerospace and energy applications. However, its high crack sensitivity limits widespread use. To address this issue, the present work examines the effects of annealing temperature from 500 to 1300 °C on the microstructural evolution and residual stress relaxation of the alloy fabricated by selective laser melting. The results reveal that no γ′ precipitates form below 800 °C, while fine coherent γ′ particles with an average size of about 115 nm emerge at 900 °C and coarsen to approximately 300 nm at 1000 °C, where crack density reaches its maximum. Further heating promotes γ′ coarsening, partial dissolution, and reprecipitation, producing a uniform equiaxed morphology of around 198 nm and pronounced crack healing at 1300 °C. Residual stresses decrease sharply with increasing temperature and nearly vanish above 1200 °C due to diffusion- and recrystallization-assisted relaxation. Electron backscatter diffraction analysis confirms a transition from partial recrystallization of about 25 % to nearly complete recrystallization of approximately 90 % between 1100 and 1300 °C. The hardness evolution follows three distinct regimes: stress-relaxation softening, γ′-strengthening, and recrystallization recovery. These findings provide important references for optimizing post-annealing treatments and enhancing the structural integrity of selective laser melted ZGH452 alloy.